In a typical motor vehicle powertrain, the engine is connected to an automatic transmission and drive axle through a fluid coupling, such as a torque converter. A clutch internal to the torque converter (referred to herein as a torque converter clutch or TCC) is selectively engageable to control or eliminate slippage between the torque converter input (impeller) and output (turbine). The TCC comprises a plate connected to rotate with the turbine in proximity to a rotary housing (input shell) of the torque converter.
When fluid is supplied to the torque converter at a point between the clutch plate and the input shell (release chamber), the fluid flows around the plate before being exhausted to an oil cooler, thereby biasing the clutch plate away from the input shell for normal (open) converter operation. When the fluid supply connections are altered to reduce the fluid pressure in the release chamber relative to the pressure on the other side of the clutch plate (apply chamber), the pressure differential across the clutch plate moves the clutch plate toward the input shell, bringing a friction pad formed on the clutch plate into contact with the input shell, engaging the TCC.
Under most conditions, smooth engagement and torque capacity control of the TCC can be achieved through a combination of open-loop and closed-loop control of the pressure differential across the clutch plate. Under certain conditions, however, the fluid flow around the clutch plate approaches the flow of the actuator, and the desired pressure differential is not achieved. In this case, TCC engagement does not occur until the flow condition is corrected. Even if closed-loop pressure controls are employed to augment the pressure differential, the TCC engagement is not initiated in a timely manner, and there may be undesired driveline torque disturbances when the engagement eventually occurs.